FISH was the more frequently used ancillary test for EWSR1-rearranged neoplasms, often because FISH can be performed with scanty amounts of material (using sections cut at 1–4 μm thickness), compared with RT–PCR which initially required sections cut at 20 μm to isolate sufficient RNA (although this is no longer the case, with 3–5 μm sections now routinely used). This evidence concerns the gene EWSR1 and neoplasm.